The US Department of Defense has estimated at $3.5bn the costs of clearing military ops out of 25MHz of radio spectrum to make way for mobe operators – except it doesn't want to march off entirely, demanding instead that the band's new owners share nicely.

Following a June 2010 edict from President Obama calling on US government agencies to make their spectrum available for commercial use, the Department of Defense reluctantly offered up the first 25MHz of the 1755-1850 MHz band - the 1755-1780 sub-band - to mobile operators. However, the DoD says it will need $3.5bn to shift operations into the upper 70 MHz (1780-1850) of adjacent spectrum, which it also owns.

Earlier testimony by the an associate administrator in the Office of Spectrum Management at NTIA estimated the cost of the move at $18bn over 10 years.

The mobe industry welcomed the offer but wanted to tie the auction of that band with the 2155MHz–2180MHz band, which is also being auctioned off by the Federal Communications Commission (FCC). A combined auction of the two bands could triple their value to $12bn.

Yet the DoD was unhappy about offering up the 1755MHz band, claiming that drones and other networked military hardware operating in that band would need to be retuned at a cost of $3.5bn. This includes $272m in direct implementation costs, $400m for the “growth” of the drone program, and $100m to compress other projects into alternative bands owned by the DoD.

Despite demanding billions of dollars to cover the cost of moving out of 1755MHz, the DoD wants to stay put – and is only offering to share the band with its new owners rather than leaving it altogether.

Even this is a significant concession from the DoD, who previously ruled out any clearing of the band at all despite the FCC's intention to get the block into an auction by September next year. The DoD does own the next 70MHz of spectrum up from 25MHz sub-band, and has offered to move parts of its operations up there out of the way, but the FCC wants the 1755MHz band cleared altogether.

Operators like paired spectrum so they can use one frequency for sending and another for receiving. It reminds them of the old days when voice calls were sent and received over separate wires, though in these days of asymmetrical data it makes more sense to use a single band for both transmit and receive, flipping between the two like a walkie-talkie; only much, much faster.

That's called Time Division Duplex (TDD, often reduced to TD as in "TD-LTE") and is being deployed in the USA by Clearwire. The problem is that traditional operators will pay more for paired spectrum and have no interest in promoting TD-LTE - as it permits disruptive players to exploit smaller blocks of spectrum. As long as the regulators are driven to get maximum auction bids, then paired spectrum will remain the default even if half of it remains unused most of the time.

In the UK Vodafone bought a decent chunk of unpaired 4G spectrum, and it will be very interesting to see how it gets used.

The UK has also taken a different route to military spectrum. Rather than asking the MoD how much it would cost to clear bands which were allocated to it, Ofcom now bills the military for its use based on estimated market value, which is proving reasonably effective in getting them into private ownership.

The sharing offer from the US military has been cautiously welcomed by both the network operators and the National Association of Broadcasters, but until details of how the sharing will work are revealed, and what services the DoD plans to leave operating in the band, it's impossible for anyone to commit further. ®